Ethanolic Gracilaria fisheri Extract and Purified N-Benzylcinnamamide Inhibit Staphylococcus epidermidis Adhesion and Biofilm Formation on Device-Relevant Surfaces

<i>Staphylococcus epidermidis</i> is a leading opportunistic pathogen in medical device-associated infections due to its ability to adhere to abiotic materials and develop biofilms that are difficult to eradicate. This study investigated the antibiofilm potential of an ethanolic extract of the red seaweed <i>Gracilaria fisheri</i> and its purified constituent, N-benzylcinnamamide, against <i>S. epidermidis</i>. Antibacterial activity was determined, and antibiofilm effects were assessed using the crystal violet assay and confocal laser scanning microscopy (CLSM). Early bacterial adhesion on glass and polyurethane (PU) surfaces was measured. The effect on catheter-associated biofilms was evaluated by scanning electron microscopy (SEM). Transcripts of biofilm- and quorum-sensing-associated genes (<i>icaA</i> and <i>luxS</i>) were assessed by semi-quantitative RT-PCR. Cytotoxicity was evaluated by MTT assay. At 200 µg/mL, biofilm biomass decreased to 48.21 ± 5.52% with the extract and to 36.65 ± 6.82% with N-benzylcinnamamide. CLSM time-course imaging showed delayed biofilm maturation and less consolidated, discontinuous structures. Surface exposure to the extract markedly reduced early attachment on both materials. On PU catheter segments, SEM demonstrated that N-benzylcinnamamide markedly reduced surface coverage and disrupted three-dimensional biofilm architecture. At the molecular level, transcription of <i>icaA</i> and <i>luxS</i> was reduced. Both the extract and N-benzylcinnamamide showed minimal cytotoxicity in HeLa cells. These findings support further evaluation of these marine-derived agents as candidates for antibiofilm surface treatments to reduce early medical device colonization.